A confidential study commissioned by the government's Youth Justice Board after the death of a 15-year-old boy claims the way children are being restrained in young offender institutions is putting them at risk.

The report, leaked to The Observer, states young offenders 'report that they frequently experience difficulty in breathing during restraint. There have been numerous reports from trainees indicating that many had experienced physical distress, difficulty breathing and other distress during restraints.'

The Review of Physical Control in Care and Behaviour Management in Secure Training Centres also said: 'Of those skills used, a number are unsafe and should be removed from the programme.' Staff were alleged to 'often manipulate an incident' so that they are legally allowed to use force. It gives a typical example in which a staff member initiates a 'low level of physical contact'.

The report was commissioned by the YJB, the body that oversees the institutions, in response to the death of 15-year-old Gareth Myatt in 2004, but has never been published. Myatt choked on his vomit after being restrained at Rainsbrook centre in Northamptonshire.

An inquest into Myatt's death earlier this year recorded a verdict of accidental death but was critical of the role played by the YJB and Rebound ECD, the private company that runs Rainsbrook.

The leaked report found that in some centres as many as '30 per cent' of restraint techniques were used to overcome 'non-compliance, specifically resistance to going to bed or moving from one location to another'. The findings suggest the institutions could be breaking the law. According to the Children Act 1989, 'force should not be used... simply to secure compliance with staff instructions'.

At Hassockfield secure training centre in Co Durham, almost a quarter of restraint techniques result in an injury to the offender, according to the report which recommended outlawing the use of a number of techniques.

The whole issue is the subject of mounting controversy because the Ministry of Justice wants to change the law allowing for physical intervention as a 'last resort'. The government says it is updating the law to provide clarification to those working with young offenders, but MPs and children's charities are concerned it will mean an expansion in the use of restraint techniques.

Sally Keeble, Labour MP for Northampton North, will initiate a parliamentary debate on Thursday on the use of restraint. 'What happened to Gareth was an absolute disgrace, it should never have happened,' she said. 'The failings of the system are astonishing. The YJB needs to be better scrutinised and possibly reformed so it doesn't just commission services but ensures they are safe.'

Last week the government was forced to admit oxygen had to be administered to offenders at Rainsbrook on four occasions in 2005 and once in 2006, following the use of restraint.

An inquest into the suicide of 14-year-old Adam Rickwood, the youngest person to die in custody in Britain, found restraint was used for non-compliance.

Last night campaigners called for action. 'The only way to prevent the suffering of children in custody and to ensure that more do not die or are injured is to conduct a public inquiry with the proper involvement of families,' said Deborah Coles, director of Inquest, the group that investigates deaths in custody.

In a statement, the YJB said the report 'was part of a wide-ranging programme of activity around behaviour management in the secure estate and was never intended for publication'. It was offered as evidence at Gareth Myatt's inquest which ended last week.